New Method to Understand Superconductors

Researchers at The Open University have devised a new method to understand the processes that happen when atoms cool which could lead to new materials for superconducting power grids and widespread use of magnetic resonance imaging (MRI).In a paper, “Bilayers of Rydberg atoms as a quantum simulator for unconventional superconductors” just published in Physical Review Letters, Dr Jim Hague and Dr Calum McCormick at The Open University’s Department of Physical Sciences describe a new method to understand the cooling of atoms, which is to simulate a superconductor using a “quantum simulator” (a kind of bespoke quantum computer for examining specific problems) rather than a supercomputer.

The researchers found that just such a simulator can be built to examine atoms cooled to just a millionth of a degree above absolute zero. The atoms are controlled using laser beams which enhance the electrical forces between the atoms, which are usually weak and unimportant. These forces mimic the physics of the superconductor, and the proposed simulator includes far more physical detail than ever before.

“The problem is that up to now nobody knew how to build such a material because physics of the best superconductors are extremely difficult to understand,” said Dr Hague. “By studying the atoms in the quantum simulator, we expect that it will be possible to make major progress in unravelling the underlying theory of these fascinating materials. A superconductor (a material with no electrical resistance) operating close to room temperature would offer potentially revolutionary technology.”

 

courtesy: science daily

Copper, Gold and Tin for Efficient Chips

With gold, copper or tin and special galvanizing processes, scientists are improving the function of semi-conductors and making the manufacture of microelectronic systems a child’s play. Especially the LED industry could profit from this.They are particularly small, durable and economical: LEDs have conquered the automotive industry; it is already possible today to recognize the make of a car by the design of the LED headlights. Whether in the interior, displays, infotainment system or brake lights, parking lights or fog lights — a modern car offers many possibilities for LED technology to be used for lighting. Unlike the traditional halogen or xenon lights, light emitting diodes need LED drivers. Their most important task: they must continuously supply the light diodes with power. In addition, they are to carry out complex tasks and to control, for example, several LEDs in series, or switch individual ones on in multiple stages if the interior lighting is to be dimmable.

Copper, Gold and Tin for Efficient Chips

An employee at the MST Lab & Fab, where the post processing of chips takes place. (Credit: © Fraunhofer IMS)

The requirements relating to the drivers are enormous: they must be immune to the high temperature and voltage differences in a car or be resistant to aggressive chemicals. In order to guarantee reliable luminosity, a higher voltage must flow through the circuits of the LED drivers. Researchers from the Fraunhofer Institute for Microelectronic Circuits and Systems IMS offer manufacturers a process to manufacture the chips that suit these applications: it is based on galvanization, a process in the semiconductor industry, in which special metals are deposited on the semiconductors.

Copper for increased current flow

However, Prof. Holger Vogt’s department at the IMS, is backing copper, in particular. “This way, we can have more current flow through the chips,” explains Vogt. That is important, because for most applications the chips must become smaller and smaller — the current that flows through them, however, stays the same. However, integrating new materials, such as a layer of copper, is not always without problems, since there are limits to the regular processes for manufacturing chips. It is for this reason that the scientists at the IMS specifically constructed a manufacturing line for “post processing” — the MST Lab & Fab — to be able to subsequently improve the chips on the substrate wafers, depending on the requirements of the application.

In addition to copper, the engineers are also able to deposit other metals or compounds such as copper-tin or gold-tin onto the chips. “These layers can be soldered,” explains Vogt. That offers a substantial advantage: the cover can be soldered onto the chip, right there on the wafer. “The result is the smallest housing for a chip that can be had,” says Vogt. It can be used to surround and protect sensitive sensors without negatively affecting their functionality. One example is bolometers, sensors that are used to measure temperature. Because the housings for bolometers must additionally also be put into a vacuum environment to provide accurate measurements, their manufacture to date has been very complex and thus expensive. However, with the help of the MST Lab & Fab, housings that are cost-effective and therefore suitable for mass production can be manufactured.

In addition, the researchers in the MST Lab & Fab have been able to construct complex components within a single housing. The are able to solder two chips, such as an opto-chip with highly sensitive photo sensors with a CMOS-Chip (Complementary Metal Oxide Semiconductor) which can measure individual photons, to each other, using the copper galvanization process. Such microelectronic components are suitable for night-vision devices or for low-light microscope applications.

Source: Science Daily

 

 

3-D Movies in Your Living Room, Without the Glasses

New television screens will make it possible for viewers to enjoy three-dimensional television programming without those bothersome 3-D glasses. Still, the content has been rather lacking — until now. A new technology will soon be adapting conventional 3-D films to the new displays in real time.

Researchers will unveil this technology in Berlin at this year’s IFA trade show from August 31 to September 5.

Lounging on a sofa while watching a 3-D movie is an exquisite pleasure for many film fans. Be that as it may, those nettlesome 3-D glasses might diminish the fun somewhat. That’s why television manufacturers are working on displays that can recreate the spellbinding magic of three-dimensional television images — without the glasses. Though prototypes of these TV screens already exist, consumers will not have to wait much longer for the market introduction of these autostereoscopic displays. Neverthe-less, the content might be a bit problematic: The 3-D movies currently available on Blu-ray are based on two different perspectives, i.e., two images, one for each eye. However, autostereoscopic displays need five to ten views of the same scene (depending on the type). In the future, the number will probably be even more. This is because these displays have to present a three-dimensional image in such a manner that it can be seen from different angles — indeed, there is more than one place to sit on a sofa, and you should be able to get the same three dimensional impressions from any position.

Researchers at Fraunhofer Institute for Telecommunications, Heinrich-Hertz Institute, HHI in Berlin recently developed a technology that converts a Blu-ray’s existing 3-D content in a manner that enables them to be shown on autostereoscopic displays. “We take the existing two images and generate a depth map — that is to say, a map that assigns a specific distance from the camera to each object,” says Christian Riechert, research fellow at HHI. “From there we compute any of several intermediate views by applying depth image-based rendering techniques. And here’s the really neat thing: The process operates on a fully automated basis, and in real time.” Previous systems were only capable of generating such depth maps at a dramatically slower pace; sometimes they even required manual adaption. Real-time conversion, by contrast, is like simultaneous interpretation: The viewer inserts a 3-D Blu-ray disc, gets comfortable in front of the TV screen and enjoys the movie — without the glasses. Meanwhile, a hardware component estimates the depth map in the background and generates the requisite views. The viewer is aware of nothing: He or she can fast forward or rewind the movie, start it, stop it — and all with the same outstanding quality. The flickering that could appear on the edges of objects — something that happens due to imprecise estimations — is imperceptible here.

The researchers have already finished the software that converts these data. In the next step, the scientists, working in collaboration with industry partners, intend to port it onto a hardware product so that it can be integrated into televisions. Nevertheless, it will still take at least another calendar year before the technology hits department store shelves.

World’s Smallest Semiconductor Laser

Physicists at The University of Texas at Austin, in collaboration with colleagues in Taiwan and China, have developed the world’s smallest semiconductor laser, a breakthrough for emerging photonic technology with applications from computing to medicine.Miniaturization of semiconductor lasers is key for the development of faster, smaller and lower energy photon-based technologies, such as ultrafast computer chips; highly sensitive biosensors for detecting, treating and studying disease; and next-generation communication technologies.

Such photonic devices could use nanolasers to generate optical signals and transmit information, and have the potential to replace electronic circuits. But the size and performance of photonic devices have been restricted by what’s known as the three-dimensional optical diffraction limit.

“We have developed a nanolaser device that operates well below the 3-D diffraction limit,” said Chih-Kang “Ken” Shih, professor of physics at The University of Texas at Austin. “We believe our research could have a large impact on nanoscale technologies.”

In the current paper, Shih and his colleagues report the first operation of a continuous-wave, low-threshold laser below the 3-D diffraction limit. When fired, the nanolaser emits a green light. The laser is too small to be visible to the naked eye.

The device is constructed of a gallium nitride nanorod that is partially filled with indium gallium nitride. Both alloys are semiconductors used commonly in LEDs. The nanorod is placed on top of a thin insulating layer of silicon that in turn covers a layer of silver film that is smooth at the atomic level.

It’s a material that the Shih lab has been perfecting for more than 15 years. That “atomic smoothness” is key to building photonic devices that don’t scatter and lose plasmons, which are waves of electrons that can be used to move large amounts of data.

“Atomically smooth plasmonic structures are highly desirable building blocks for applications with low loss of data,” said Shih.

Nanolasers such as this could provide for the development of chips where all processes are contained on the chip, so-called “on-chip” communication systems. This would prevent heat gains and information loss typically associated with electronic devices that pass data between multiple chips.

“Size mismatches between electronics and photonics have been a huge barrier to realize on-chip optical communications and computing systems,” said Shangjr Gwo, professor at National Tsing Hua University in Taiwain and a former doctoral student of Shih’s.

Entropy Paving the Route to Nanostructures

Researchers trying to herd tiny particles into useful ordered formations have found an unlikely ally: entropy, a tendency generally described as “disorder.”Computer simulations by University of Michigan scientists and engineers show that the property can nudge particles to form organized structures. By analyzing the shapes of the particles beforehand, they can even predict what kinds of structures will form.The findings, published in this week’s edition of Science, help lay the ground rules for making designer materials with wild capabilities such as shape-shifting skins to camouflage a vehicle or optimize its aerodynamics.

Shapes can arrange themselves into crystal structures through entropy alone, new research from the University of Michigan shows. (Credit: P. Damasceno, M. Engel, S. Glotzer)

Physicist and chemical engineering professor Sharon Glotzer proposes that such materials could be designed by working backward from the desired properties to generate a blueprint. That design can then be realized with nanoparticles — particles a thousand times smaller than the width of a human hair that can combine in ways that would be impossible through ordinary chemistry alone.

One of the major challenges is persuading the nanoparticles to create the intended structures, but recent studies by Glotzer’s group and others showed that some simple particle shapes do so spontaneously as the particles are crowded together. The team wondered if other particle shapes could do the same.

“We studied 145 different shapes, and that gave us more data than anyone has ever had on these types of potential crystal-formers,” Glotzer SAID. “With so much information, we could begin to see just how many structures are possible from particle shape alone, and look for trends.”

Using computer code written by chemical engineering research investigator Michael Engel, applied physics graduate student Pablo Damasceno ran thousands of virtual experiments, exploring how each shape behaved under different levels of crowding. The program could handle any polyhedral shape, such as dice with any number of sides.

Left to their own devices, drifting particles find the arrangements with the highest entropy. That arrangement matches the idea that entropy is a disorder if the particles have enough space: they disperse, pointed in random directions. But crowded tightly, the particles began forming crystal structures like atoms do — even though they couldn’t make bonds. These ordered crystals had to be the high-entropy arrangements, too.

.Glotzer explains that this isn’t really disorder creating order — entropy needs its image updated. Instead, she describes it as a measure of possibilities. If you could turn off gravity and empty a bag full of dice into a jar, the floating dice would point every which way. However, if you keep adding dice, eventually space becomes so limited that the dice have more options to align face-to-face. The same thing happens to the nanoparticles, which are so small that they feel entropy’s influence more strongly than gravity’s.

“It’s all about options. In this case, ordered arrangements produce the most possibilities, the most options. It’s counterintuitive, to be sure,” Glotzer said.

The simulation results showed that nearly 70 percent of the shapes tested produced crystal-like structures under entropy alone. But the shocker was how complicated some of these structures were, with up to 52 particles involved in the pattern that repeated throughout the crystal.

“That’s an extraordinarily complex crystal structure even for atoms to form, let alone particles that can’t chemically bond,” Glotzer said.

The particle shapes produced three crystal types: regular crystals like salt, liquid crystals as found in some flat-screen TVs and plastic crystals in which particles can spin in place. By analyzing the shape of the particle and how groups of them behave before they crystallize, Damasceno said that it is possible to predict which type of crystal the particles would make.

“The geometry of the particles themselves holds the secret for their assembly behavior,” he said.

Why the other 30 percent never formed crystal structures, remaining as disordered glasses, is a mystery.

“These may still want to form crystals but got stuck. What’s neat is that for any particle that gets stuck, we had other, awfully similar shapes forming crystals,” Glotzer said.

In addition to finding out more about how to coax nanoparticles into structures, her team will also try to discover why some shapes resist order.

Toward Achieving One Million Times Increase in Computing Efficiency

Modern-day computers are based on logic circuits using semiconductor transistors. To increase computing power, smaller transistors are required. Moore’s Law states that the number of transistors that can fit on an integrated circuit should double every two years due to scaling. But as transistors reach atomic dimensions, achieving this feat is becoming increasingly difficult.

Present-day computer server room. Modern-day computers are based on logic circuits using semiconductor transistors. (Credit: © Scanrail / Fotolia)

Among the most significant challenges is heat dissipation from circuits created using today’s standard semiconductor technology, complementary metal-oxide semiconductor (CMOS), which give off more heat as more transistors are added. This makes CMOS incapable of supporting the computers of the future.

Engineers are therefore seeking alternatives to CMOS that would allow for highly efficient computer logic circuits that generate much less heat. Northwestern University researchers may have found a solution: an entirely new logic circuit family based on magnetic semiconductor devices. The advance could lead to logic circuits up to 1 million times more power-efficient than today’s.

Unlike traditional integrated circuits, which consist of a collection of miniature transistors operating on a single piece of semiconductor, the so-called “spin logic circuits” utilize the quantum physics phenomenon of spin, a fundamental property of the electron.

“What we’ve developed is a device that can be configured in a logic circuit that is capable of performing all the necessary Boolean logic and can be cascaded to develop sophisticated function units,” said Bruce W. Wessels, Walter P. Murphy Professor of Materials Science and Engineering, one of the paper’s authors. “We are using ‘spintronic’ logic devices to successfully perform the same operations as a conventional CMOS circuits but with fewer devices and more computing power.”

The spin-logic circuits are created with magnetoresistive bipolar spin-transistors, recently patented by McCormick researchers.

A paper describing the findings, “Emitter-Coupled Spin-Transistor Logic,” was presented July 5 at the International Symposium on Nanoscale Architectures held in the Netherlands. Additional Northwestern authors include graduate student Joseph Friedman, the paper’s lead author; Gokhan Memik, associate professor of electrical engineering and computer science; and Alan Sahakian, professor of electrical engineering and computer science.

The new logic family, which takes advantage of the magnetic properties associated with electron spin, could result in a computer 1 million times more power-efficient than those on the market today. While that achievement is optimistic and could take a decade to realize, “We think this is potentially groundbreaking,” Friedman said.

Highly Conductive and Elastic Conductors Created Using Silver Nanowires

Researchers from North Carolina State University have developed highly conductive and elastic conductors made from silver nanoscale wires (nanowires). These elastic conductors can be used to develop stretchable electronic devices.Stretchable circuitry would be able to do many things that its rigid counterpart cannot. For example, an electronic “skin” could help robots pick up delicate objects without breaking them, and stretchable displays and antennas could make cell phones and other electronic devices stretch and compress without affecting their performance. However, the first step toward making such applications possible is to produce conductors that are elastic and able to effectively and reliably transmit electric signals regardless of whether they are deformed.

The silver nanowires can be printed to fabricate patterned stretchable conductors. (Credit: Image courtesy of North Carolina State University)

Dr. Yong Zhu, an assistant professor of mechanical and aerospace engineering at NC State, and Feng Xu, a Ph.D. student in Zhu’s lab have developed such elastic conductors using silver nanowires.

Silver has very high electric conductivity, meaning that it can transfer electricity efficiently. And the new technique developed at NC State embeds highly conductive silver nanowires in a polymer that can withstand significant stretching without adversely affecting the material’s conductivity. This makes it attractive as a component for use in stretchable electronic devices.

“This development is very exciting because it could be immediately applied to a broad range of applications,” Zhu said. “In addition, our work focuses on high and stable conductivity under a large degree of deformation, complementary to most other work using silver nanowires that are more concerned with flexibility and transparency.”

“The fabrication approach is very simple,” says Xu. Silver nanowires are placed on a silicon plate. A liquid polymer is poured over the silicon substrate. The polymer is then exposed to high heat, which turns the polymer from a liquid into an elastic solid. Because the polymer flows around the silver nanowires when it is in liquid form, the nanowires are trapped in the polymer when it becomes solid. The polymer can then be peeled off the silicon plate.

“Also silver nanowires can be printed to fabricate patterned stretchable conductors,” Xu says. The fact that it is easy to make patterns using the silver nanowire conductors should facilitate the technique’s use in electronics manufacturing.

When the nanowire-embedded polymer is stretched and relaxed, the surface of the polymer containing nanowires buckles. The end result is that the composite is flat on the side that contains no nanowires, but wavy on the side that contains silver nanowires.

After the nanowire-embedded surface has buckled, the material can be stretched up to 50 percent of its elongation, or tensile strain, without affecting the conductivity of the silver nanowires. This is because the buckled shape of the material allows the nanowires to stay in a fixed position relative to each other, even as the polymer is being stretched.

“In addition to having high conductivity and a large stable strain range, the new stretchable conductors show excellent robustness under repeated mechanical loading,” Zhu says. Other reported stretchable conductive materials are typically deposited on top of substrates and could delaminate under repeated mechanical stretching or surface rubbing.